1. Field of the Invention
The present invention relates to a liquid jet head and a liquid jet apparatus, and more particularly, to an inkjet recording head and an inkjet recording apparatus, in which a part of pressure generating chambers which communicate with nozzle orifices ejecting ink droplets is formed of a vibration plate, piezoelectric elements are formed on a surface of this vibration plate, and the ink droplets are ejected by displacement of the piezoelectric elements.
2. Description of the Related Art
In an inkjet recording head, a part of pressure generating chambers communicating with nozzle orifices ejecting ink droplets is formed of a vibration plate, this vibration plate is deformed by piezoelectric elements, ink in pressure generating chambers is pressurized and thus ink droplets are ejected from nozzle orifices. There are two types of inkjet recording heads which have been put to practical use, which include: one using a piezoelectric actuator of a longitudinal vibration mode, which extends and contracts in an axial direction of a piezoelectric element; and one using a piezoelectric actuator of a flexure vibration mode.
As the one using the actuator of the flexure vibration mode, there is one, for example, in which a uniform piezoelectric material layer is formed across an entire surface of a vibration plate by use of a deposition technology, this piezoelectric material layer is cut into a shape corresponding to pressure generating chambers by use of a lithography method, and piezoelectric elements are formed so as to be independent for each of the pressure generating chambers (for example, see Patent Document 1) Moreover, the piezoelectric element used in the above-described actuator of the flexure vibration mode includes a lower electrode that is a common electrode, a piezoelectric layer formed on the lower electrode and an upper electrode that is an individual electrode formed on the piezoelectric layer.
In such a conventional inkjet recording head, the lower electrode is provided so as to be common to a plurality of piezoelectric elements. Thus, when a number of ink droplets are ejected all at once by simultaneously driving a number of piezoelectric elements, a voltage drop occurs and a displacement amount of the piezoelectric elements becomes unstable. Consequently, there arises a problem that an ink ejecting property is deteriorated. Moreover, if the piezoelectric elements are arranged densely, for example, it is required to narrow a width of wiring drawn out from the lower electrode between the piezoelectric elements. Accordingly, when the Wiring width is narrowed, wiring resistance (resistance value) is increased, thus causing such problem as described above.
Moreover, since the lower electrode formed of a thin film has a thin film thickness, the wiring resistance is increased as in the case of narrowing the wiring width. Thus, there arises a problem that the ink ejecting property is deteriorated. Note that this problem can be solved by forming the lower electrode to have a large film thickness. However, the lower electrode serves also as a vibration plate in a region facing the pressure generating chambers. Accordingly, when the film thickness of the lower electrode is increased, there arises a problem that a displacement amount of the vibration plate due to drive of the piezoelectric element is lowered. Note that, needless to say, such problems as described above similarly arise not only in the inkjet recording head ejecting ink droplets but also in other liquid jet heads ejecting liquid droplets other than ink.
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-225290 (Page 5, FIGS. 1 and 2)